GN: Update heap stubs for android

Source/platform/heap/asm/BUILD.gn

+# Copyright 2014 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+if (cpu_arch == "x86" || cpu_arch == "x64") {
+import("//third_party/yasm/yasm_assemble.gni")
+
+yasm_assemble("asm") {
+  assert(cpu_arch == "x86" || cpu_arch == "x64")
+
+  sources = [ "SaveRegisters_x86.asm" ]
+
+  yasm_flags = []
+  if (is_mac) {
+    # Necessary to ensure symbols end up with a _ prefix; added by
+    # yasm_compile.gypi for Windows, but not Mac.
+    yasm_flags += [ "-DPREFIX" ]
+  }
+  if (cpu_arch == "x64") {
+    if (is_win) {
+      yasm_flags += [ "-DX64WIN=1" ]
+    } else {
+      yasm_flags += [ "-DX64POSIX=1" ]
+    }
+  } else {  # cpu_arch == "x86"
+    yasm_flags += [ "-DIA32=1" ]
+  }
+}
+
+} else { # cpu_arch == "x86" || cpu_arch == "x64"
+
+source_set("asm") {
+  if (cpu_arch == "arm") {
+    sources = [ "SaveRegisters_arm.S" ]
+  } else if (cpu_arch == "arm64") {
+    sources = [ "SaveRegisters_arm64.S" ]
+  } else if (cpu_arch == "mipsel") {
+    sources = [ "SaveRegisters_mips.S" ]
+  }
+
+  if (cpu_arch == "arm") {
+    defines = [ "ARM=1" ]
+  }
+}
+
+} # cpu_arch == "x86" || cpu_arch == "x64"
+
+